This invention relates to a method for minimizing slag carryover during tapping of molten metal from a furnace, and to an article for use in the method.
It is desirable in order to improve ladle addition recoveries and deoxidation control in steelmaking to minimize carryover of slag with the molten metal as it is tapped from the furnace. Various stopper devices have been used for plugging the taphole of BOP and Q-BOP furnaces to prevent drainage of slag at the beginning of tap when the furnace is first tilted downward to drain the metal out. However, most of the slag gets into the ladle as a result of becoming entrained with the metal in a vortex which forms at the taphole entrance as the final portion of metal is drained from the furnace.
Two different approaches have been made toward solving this latter problem. In one, a device located on the exterior of the furnace is actuated to physically cut off the stream as slag begins to flow out of the taphole. A second approach has been to insert a floatable device into the furnace which acts as a stopper becoming lodged in the taphole. These latter devices float at the slag-metal interface and tend to prevent formation of a vortex, thus decreasing slag entrainment. However, the floatable stoppers have the disadvantage that they tend to weld to the wall of the taphole and are difficult to dislodge, requiring burning with an oxygen lance and causing loss of time between heats. This also increases wear on the taphole itself. Examples of prior floatable stoppers are shown in Stahl Und Eisen, Volume 90, pages 257-263 and Japanese Patent Application No. J47-20803.
It is the primary object of this invention to overcome the disadvantages of the above-mentioned prior art and to provide an improved floatable device for minimizing slag carryover from a furnace during tapping of molten metal therefrom and a method for use of the new device.